Typically, as the method of measuring quality of a communication network, there are two methods of an active measuring method and a passive measuring method. The active measuring method is a method of estimating the quality of the network by transmitting a test packet to the network and detecting delay and loss of the packet. On the other hand, the passive measuring method is a method of estimating the quality of the network by monitoring the state of a packet flowing through the network without transmitting any test packet. Each of them has a drawback and an advantage, and there are various specific attaining methods.
For example, in Japanese Patent Application Publication (JP-P2002-64545A) (Related Art 1) is described a passive measuring method, in which in a network system where a voice packet is transmitted from a communication system to a communication terminal through a packet communication network, the qualities such as a packet loss rate in an end-to-end (E2E) and a variation time of the voice packet between the communication system and the communication terminal are measured based on an RTCP-RR (RTP (Real-time Transport Protocol) Control Protocol-Receiver Report) packet that is returned from the communication terminal to the communication system.
Also, in Japanese Patent Application Publication (JP-P2005-210515A) (Related Art 2) is described a packet measuring method, in which a certain one point between a transmission terminal and a reception terminal is defined as a passive measurement point, and a flow between the start and end of communication between the transmission and reception terminals is extracted, and a quality data including a data of a packet loss in E2E between the transmission terminal and the reception terminal is estimated from a time series data of packet arrival at the reception terminal based on a header data having the sequence number of the packet.
On the other hand, a technique has been conventionally proposed in which degradation of flow quality is determined from a quality data of a flow through the network so as to estimate a degradation portion. For example, in Japanese Patent Application Publication (JP-P2002-271392A) (Related Art 3) is described a method of determining flows of good quality and flows of bad quality based on quality data of communication flows and a predetermined quality threshold, determining a link through which the flows of bad quality pass based on route data, and estimating a link on which the route data of the flows of bad quality overlap, as a quality degradation portion.
In a current communication network system, a plurality of networks that are managed by corporations different from each other are connected to each other, to form a large network. In such a communication network system, communication is carried out between terminals connected to different networks in addition to communication between terminals connected to the same network. The communication quality in case of the communication between the terminals connected to different networks is determined based on the communication qualities of all the networks on the route, and when the quality is deteriorated in any one network, the quality of the entire flow is deteriorated. Thus, a network manager of each network is required to early detect the degradation and carry out necessary countermeasure.
When the network manager of each network measures E2E flow quality data between transmitting and receiving terminals, which are connected to the network administrated by the network manager, by the passive measuring method in order to detect degradation in the communication quality in the network administrated by the network manager, if the degradation of quality is detected in the E2E flow quality data between the transmitting and receiving terminals, the network manager can instantly determine that there is a cause in the network. However, when any one of the terminals is connected to another network, the network manager cannot determine whether a cause exists in the network or the other network, even if the degradation of quality is detected in the E2E flow quality data between the transmitting and receiving terminals. This reason is that even if the quality degradation exists in the network, or the quality degradation exists in the other network, the measured E2E flow quality data exhibits the degradation in both the cases.
Also, when by applying the technique indicated in the related art 3 to the flow extending over the plurality of networks, and determining links through which the flow of the bad quality passes from the route data, one of the links in which the route data of flows of the had qualities overlap is estimated as a quality degradation portion, it is possible to determine whether the quality degradation portion exists in the network or in another network. However, although the route data of the network managed by a certain network manager can be generally used by the network manager, the route data of the network that is not managed by the network manager itself (the other network) cannot be used by the network manager. Thus, it is difficult to apply the technique indicated in the related art 3 to the flow extending over the plurality of networks.
In this way, among the E2E flow quality data which is measured by the passive measuring method in communication between the transmitting and receiving terminals, the E2E flow quality data when any one of the transmitting and receiving terminals exists in another network cannot be conventionally used for the quality management of the network at all.